Abstract:
Sri Lanka is known the world over for its wide variety of coloured gemstones. In
addition to the good quality gemstones, low-quality gemstones (Geuda) are found in
Sri Lanka. Heat treatment is a physicochemical method to improve the colour and
clarity of these low-quality gemstones. This study aims to conduct investigations
based on chemical and spectrophotometric analysis in order to develop well-defined
procedures to enhance the quality (colour and clarity) of the low-quality gemstones,
namely Geuda, Ottu, Kahata and dark tourmaline. Low-quality gem samples were
collected from two gem pits in Marapana, Ratnapura. Based on the initial
characterisation, the gem samples were grouped in to four categories: Geuda, Ottu,
Rambaha and Spinel and their weight ranged from 0.3 to 7 carrots. The size of the
collected gems was ranged 4 - 12 mm. Initial observations were derived by using
magnifying lenses which suggested that the majority of the samples contained
mineral inclusions, cracks and had a semi-transparent appearance, therefore they
possessed a low commercial value in the market. Further, characterizations of the
samples were subjected to determine the physical properties (refractive index and
specific gravity) and chemical properties (inclusions). Spectrophotometric
properties will also be determined using Raman spectrometer, X-ray fluorescence
(XRF) spectrometer, X-ray diffraction (XRD) spectrometer, UV visible
spectrophotometer, Fourier-transform infrared spectrophotometer (FTIR) and Laser
ablation inductive couple plasma mass spectrometer (LA-ICPMS). Based on the
physical, chemical and spectrophotometric properties along with the spatial data, the
heat treatment will be conducted using Lakmini, tube and muffle furnaces. Heat
treated sample will be further investigated to identify atomic rearrangement and also
to identify optimum heat treatment conditions for low-quality gemstones.
